1. Field of the Invention
The present invention relates to a boring head of a boring machine.
2. Description of the Prior Art
A conventional boring machine includes a boring head which is connected with the boring machine through pilot tubes under ground. The boring head is normally rotated with the pilot tubes and is pushed forwardly in a longitudinal direction of the pilot tubes.
With such boring operation, however, the direction of the boring head may be deviated from a planned course. In such a case, it is necessary to correct the course of the boring head.
In such a case, a position of the boring head in both horizontal and vertical directions is measured by a depth sensor utilizing liquid or a magnetic sensor mounted within the boring head. The output of the sensor is transmitted to a wayside control device via a cable extending through the pilot tubes. The boring head includes at the forward portion thereof a rotary member which is rotatable around the longitudinal axis of the boring head by a motor disposed within the boring head and is provided with a slant surface inclined at a predetermined angle relative to a longitudinal direction. As the boring head is pushed forwardly by the boring machine, the boring head moves in the longitudinal direction when the rotary member is rotated, while the boring head moves obliquely according to the position of the slant surface when the rotary member is not rotated. Based on the output of the sensor, the control device calculates an appropriate position of the inclined surface for compensating the displacement of the position of the boring head from the planned course. The control device thereafter outputs the corresponding signal to the motor for rotation of the rotary member so as to position the slant surface at the appropriate position. After positioning the slant surface, another pilot pipe is connected with the previously connected pilot pipe for subsequent pushing operation by the boring machine.
However, the conventional device for measuring the position of the slant surface and rotating the rotary member becomes difficult to be disposed within the boring head as the boring head as well as the pilot tubes becomes to have a smaller diameter. In fact, it is substantially impossible to dispose such a device within the boring head having a diameter less than 50 mm.
Therefore, practically, the rotary member and the motor is not provided with the boring head and only the sensor and the inclined surface are provided with the boring head. In such a case, rotation of the slant surface is made by rotating the boring head with the pilot tubes by the boring machine. The angle of rotation of the boring head is determined based on the position of the slant surface when the boring operation has been started. However, the pilot tubes are normally threadably connected with each other, and therefore, the angle of rotation of the boring head to be expected does not accurately correspond to that of the angle of actual rotation of the boring head because of the possible displacement between the contiguous pilot tubes during rotation. Further, since the pilot tubes must be subsequently pushed by the boring machine from a limited space, they must have relatively short length. Therefore, the difference between the angle of rotation to be expected and that of the actual rotation of the boring head further increases. For this reason, it is not possible to accurately position the inclined surface at the appropriate position. Therefore, in the conventional device of this type, it is necessary to move the boring head at a short distance after positioning of the slant surface, and to subsequently measure the actual position of the boring head for further correction of direction when the boring head is not on the planned course.
Additionally, with the above conventional devices, it requires to pass the cable for transmitting the output of the sensor to the wayside control device, and therefore, the operation must be carefully performed not to damage the cable.